a) Field of the Invention
The present invention relates to a thermal sensor to detect water temperatures of cooling systems of automobile engines, etc.
b) Description of the Prior Art
Generally, a conventional thermal sensor to detect the water temperature of a cooling system installed on an automobile engine is, as shown in FIG. 1, a thermal sensor 23 for an Electronic Control Unit (ECU) which regulates an engine system as to the fan motor, fuel injection, ignition time, idling revolution, etc. or a thermal sensor 24 to indicate water temperatures of a cooling water of an engine on a water thermometer mounted on a panel in front of the driver's seat.
The sensors 23 and 24 have a built-in thermistor of different properties respectively. The thermal sensors 23 and 24 both are to detect the temperature of the same cooling water and each thermal sensor is installed in the same cooling water circuit 25 separately. Further, there is such a thermal sensor as disclosed in Japanese Utility Model Application No. Hei 4-46882 (Laid Open Utility Model Application No. Hei 6-7029) filed by the applicant of the present invention and the thermal sensor is set forth hereunder.
The conventional thermal sensors shown in FIG. 1 have following disadvantages.
The sensor 23 for the ECU and the sensor 24 for the water thermometer are installed separately and two holes must be provided to install two thermal sensors on the cooling water circuit 25 of the engine separately.
This requires much works for the processing of the thermal sensors and installing thereof on the cooling water circuit.
Further, it is difficult to streamline a system composing two separate thermal sensors with regard to the size and to reduce the weight of the system.
In addition, the inventory and maintenance of two thermal sensors of different types are troublesome and costly.
The thermal sensor disclosed in the Utility Model Application No. Hei 4-46882 (Laid Open Utility Model Application No. Hei 6-7029) is in a metallic case in which two thermistors are installed, the one as a thermal sensor for a ECU and the other as a thermal sensor for a water thermometer which requires much electric current to swing a compass needle of the water thermometer. As a result, the latter thermistor itself generates a quantity of heat due to the electric current input and therefore a thermal insulation is provided between two thermistors to prevent a thermal interference caused by the heat against the former thermistor as the thermal sensor for the ECU.
However, still the thermal insulation alone is insufficient to substantially reduce the thermal interference against the thermistor as the thermal sensor for the ECU.